Keskusteluraportti: Geenit ja käyttäytyminen

For the past ten years I have been a part-time science journalist. Early in 2004 I wrote a five page review article on behaviour genetics, which was published in a Finnish science periodical. The article triggered a counterblast of exceptional intensity and tone from an unexpected opponent, a professor of genetics. Here I will summarise my article and the short debate that followed.

In the article I discussed the three ”laws” of behaviour genetics (Turkheimer 2000). Law no 1: all human behavioural traits are heritable. This may be a small exaggeration, but only a small one. The law implicates that the variation between individuals is to some extent due to genetic differences. By examining twins that have been separated at birth researchers have been able to provide estimates of this so called heritability. These identical twins share all their genes but none of the environment (in relation to normal environmental variation within the sample). Heritability can also be measured, by comparing identical twins that have been raised together, with non-identical twins also raised together, and by comparisons of genetic siblings and adopted children.

Law no 2: The effects of growing up in the same family are smaller than the effects of the genes. In order to see what this means, one must distinguish between the concepts of shared and non-shared environments. The former is the environment that has the same effect on siblings (e.g. parents and neighbours). The latter refers to all the rest: everything that makes their environments unique, such as being a favourite child of the parents, illnesses etc. There are several ways to scrutinise the effects of shared and non-shared environments, all of which are rather complicated, but which were discussed in my article concisely.

Finally law no 3. The third law can be inferred from the first and the second: A significant part of the variation of complex behavioural traits is not due to genes or to effects of family environments. In other words, there are yet other reasons, that make even identical twins dissimilar personalities.

In outlining the findings of behaviour genetics, I leaned on the world’s most renowned scientists in the field, and their popularisers, especially Steven Pinker (2002) and Matt Ridley (2003). The findings in a nutshell are the following. Identical twins separated at birth bare a high resemblance. Identical twins raised together resemble each other more than non-identical twins raised together. And finally, the resemblance between genetic siblings is higher than that of children adopted to the same family.

Depending on the trait in question, heritability estimates have typically varied between 0,25 and 0,75. (Heritability can vary between zero and one. If heritability is 1, all variation can be accounted for by genetic factors, and if it is 0, all variation is of an environmental origin.) For personality traits, most behaviour geneticists agree on the following figures: about 40 percent of the variation is due to genetic factors, less than 10 percent is due to shared environments, and about 25 percent is due to unique environments that the individuals experience. The remaining is simply measurement error.

This was the factual content of my article. Namely that genes explain much of the variation between individuals, and parental upbringing does not account for nearly as much as generally presumed. Perhaps I was naive, as the attack my writing evoked took me by surprise. The professor of genetics, Petter Portin (2004) from The University of Turku titled his comment ”Skilful manipulation”.

Portin accused the laws of being ”only goal-directed and shallow tosses coming from people with political goals.” According to Portin, my article represents ”a model example of a malevolent covert indoctrination” and my ”political aims become evident toward the end of the article.” Finally, my ”colleagues”, Pinker and Ridley, ”have an easy street in today’s political atmosphere in The United States.”

Such political insinuation, or labelling even, is nothing new to those, who saw the sociobiology debates in the 1970’s and 1980’s. The article was, of course, far removed from any political themes. The only time I even mentioned politics was in my brief defending reply, where I underlined that his ”conjecture about my political orientation has no truth-value whatsoever.”
The debate, of course, died down very quickly: who would want to put their neck out for such excessive public offences? In retrospect, I readily admit that there was a sharp-worded remark concerning motives and beliefs of family therapists that was beyond my knowledge. I wrote that the significance of parental upbringing is emphasised mostly by industries that profit from emphasising it – by selling books and services. Perhaps I should have structured this comment in a more considerate manner.

* * *

After the Second World War some Japanese soldiers were forsaken in remote jungle bases without contact with the outside world. They routinely followed their watch duties and honoured the Emperor, not knowing Japan had been defeated. To me, Portin seems like this kind of ocean maroon [1] who still blindly abides to the radical activism of his youth.
Be as it may, no amount of political accusations can erase the indisputable results of twin studies. Nowadays the notion that genes and environment together shape our personalities is considered a truism. But this truism is precisely the reason why the systematic comparisons of twins and siblings provide such valuable information. The story is, of course, very different, if we change our viewpoint from individual differences to differences between species. Then genes are everything. Even our very close relatives, the chimpanzees and bonobos, if raised in human families, do not grow up to be like humans – no matter how hard we try to treat them as such.

[1] I owe my thanks to cartoon character Daffy Duck for this illustrating phrase.